Wave-signal translating apparatus



March 12, 1957 J. c. SPRACKLEN WAVE-SIGNAL TRANSLATING APPARATUSOriginal Filed Aug. 22, 1952 25 :0 62 8. E Q z j 09 E226 oc coom aw wcmm E296 ll Lo BQom oc coom 52m mfi 6 6 \5 6- mm 6:15:3 5 2mm 2 I. 2 mm mHIS ATTORNEY.

United States Patent 2,785,300 WAVE-SIGNAL TRANSLATING APPARATUS John G.Spracklen, Chicago, 11]., assignor to Zenith Radio Corporation, acorporation of Illinois Original application August 22, 1952, Serial No.305,875. Divided and this application April 5, 1954, Serial No. 420,909

4 Claims. (Cl. 250-20) This invention relates to wave-signal translatingapparatus for the amplification and demodulation of modulated Wavesignals. This application is a division of copending application, SerialNo. 305,875, filed August 22, 1952, for Wave-Signal TranslatingApparatus, and assigned to the present assignee.

In the reception of modulated wave-signals, it is conventional practiceto heterodyne the incoming radiofrequency signal with alocally-generated constant-frequency signal to provide a modulatedintermediate-frequency signal. The modulated intermediate-frequencysignal is amplified and demodulated to provide an audiofrequency orvideo-frequency signal representing the modulation components of theoriginal wave-signal, and the detected signal thus obtained is amplifiedand applied to a suitable utilization device such as a loudspeaker or animage-reproducing device. Conventionally, several cascaded stages areutilized to provide the desired intermediate-frequency amplification,and separate independent stages are ordinarily used to effectdemodulation and subsequent amplification of the modulation components.Thus, for example, in a conventional television receiver, four cascadedstages of intermediate-frequency amplification may be used, followed bya rectifier device for video-frequency demodulation and two cascadedstages of video-frequency amplification.

It is an important object of the present invention to provide novel andimproved wave-signal translating apparatus for providing in a singlestage amplification of both a modulated wave-signal and the modulationcomponents of such amplified signal after demodulation.

It is a further object of the invention to provide improved wave-signaltranslating apparatus for combining in a single stage the functions ofmodulated wave-signal amplification, demodulation, and subsequentamplification of the modulation components.

Still another object of the invention is to provide new and improvedWave-signal translating apparatus for combining in a single stage thefunctions of two or more separate and independent stages of conventionalwavesignal receivers, thereby effecting a substantial cost saving inreceiver manufacture.

In accordance with the invention, the above and other objects areachieved by providing an electron-discharge device including, in theorder named, a cathode, a first control grid, an accelerating anode, asecond control grid, and an output electrode. A source of compositetelevision signals, including video-modulated image-carrier andaudio-modulated sound-carrier components separated by a predeterminedfrequency difference, is coupled to one of the control grids and to thecathode. There is also provided a two-terminal load circuit having oneterminal coupled externally of the discharge device to the other controlgrid only and having an im edance at the image-carrier and sound-carrierfrequencies greater than the reciprocal of the eifectivetransconductance of the input control grid with res ect to the othercontrol grid for developing an amplified signal including the ice.

image-carrier and audio-modulated sound-carrier corn ponents. Means arealso coupled to the other control grid and to the cathode for effectingdemodulation of the amplified signal, whereby the image-carrier and theaudio modulated sound-carrier components of the amplified signal areintermodulated. Further means, including an output circuit tuned to anintercarrier frequency corresponding to the predetermined frequencydifierence betweent image-carrier and sound-carrier components of thecomposite television signal, are coupled to the output electrode and tothe cathode and utilize the transconductance of the other control gridwith respect to the output elecrode for developing an amplifiedaudio-modulated intercarrier-frequency output signal. Finally, means arecoupled to the output circuit for demodulating the audio-modulatedoutput signal.

The features of the present invention which are believed to be novel areset forth with particularity in the appended claims. The invention,together with further objects and advantages thereof, may best beunderstood, however, by reference to the following description taken inconnection with the accompanying drawing in which the single figure is aschematic diagram of a television receiver embodying novel wave-signaltranslating apparatus constructed in accordance with the presentinvention.

In the illustrated embodiment of the invention, incoming compositetelevision signals received by an antenna are applied through aradio-frequency amplifier 91 to an'oscillator-converter 92.Intermediate-frequency compositive television signals fromoscillator-converter 92 are applied to an intermediate-frequencyamplifier 93, which may consist for example of three or fourcascade-connected I. F. amplifier stages. Amplifier 93 is coupled to avideo detector 94, which may be of conventional construction, and thedetected composite video signals from detector 94 are amplified by avideo amplifier 95 and applied to the input circuit of a cathode-raytube 96 or other image-reproducing device. Composite video signals fromvideo amplifier 95 are also applied to a synchronizingsignal separator97, and the line-frequency and fieldfrequency synchronizing-pulsecomponents from separator 97 are employed to control line-frequency andfield frequency scanning systems 98 and 99 which, in turn, providesuitable scanning signals to line-frequency and field-frequencydeflection coils 100 and 101 respectively.

- Intermediate-frequency amplifier 93 is also coupled by means of outputcircuit 103 to wave-signal translating apparatus 104 constructed inaccordance with the present invention, where the intermediate-frequencysignals are further amplified and the video-carrier and sound-carriercomponents are intermodulated and amplified to provide an amplifiedaudio modulated intercarrier frequency sound signal. This amplifiedintercarrier-sound signal is applied to a limiter-discriminator 105, andthe resulting audio-frequency signals, after amplification in audiocircuits 106, are impressed on a loudspeaker 107 or othersound-reproducing device.

The receiver may be of conventional construction with the exception ofwave-signal translating apparatus 104. Apparatus 104 comprises a singleelectron-discharge device 108 including in the order named a cathode109, a first control grid 110, an accelerating or screen grid 111, asecond control grid 112 and an output electrode or anode 113. Anadditional screen grid 114 and a suppressor grid 115 may be providedbetween second control cluding video-carrier and audio-modulatedsound-carrier components separated by a predetermined frequency difference, are applied between first control grid and cathode 109 by meansof a coil 116 magnetically coupled for inte'rmediate-fret uencyamplification.

to output circuit 103 of intermediate-frequency amplifier 93. Cathodel09isconnected to ground through. a circuit comprising a resistor 117 and acondenser 118, and screen grids 111 and 114 are connected together andthrough a resistor 120 to the positiveterminal of a battery 119orothersource of tuiidirectionaloperating potential, the negativeterminal of which is grounded; Screen grids 111 and 114 are alsobypassed to ground by means of condenser 121. Suppressor grid 115 isdirectly connected to ground.

A two-terminal load circuit, tuned to the receiverintermediate frequencyand comprising an inductor 122 and ground and the cathode bias circuitcomprising resistor 117 and condenser 118;

Anode 113 is coupled to the positive terminal of battery 129 or othersuitable source of unidirectional operating potential through anintercarrier-frequency load circuitcomprising an inductor 130 shunted byan effective capacity 131 which may be composed of distributed circuitcapacities. Battery 129 is bypassed to ground by means of a condenser132. Anode 113 is also 'coupled to limiter-discriminator 105 by means ofa lead 133.

In operation, intermediate-frequency composite video 1 signals,including video-carrier and audio-modulated sound-carriercomponents, areimpressed on first control grid 110. It is known in the art thatWhenever a lowpotenti-al control grid is placed in the path of anelectron stream in a position following a high-potential acceleratingelectrode, a virtual cathode is produced in the vicinity of the controlgrid. As the intensity of'the elecamplified form at second control grid112 by virtueof space charge couplingfrom first control grid 110 to second control grid 112. Trapcircuit 127, also tuned to the intermediatefrequency, may be provided for the purpose of emphasizing the carriercomponents by providing a double-peaked impedance characteristic for thetwoterminal load circuit coupled to second control grid 112.

Second control grid 112 is biased to a non-linear portion of its dynamictransfer characteristic by means coupled to second control electrode112'and to cathode 1109. in the illustrated embodiment, this operatingbias is provided by cathode resistor 117 and condenser 118 and furtherby resistor 125 and. condenser 126 connected in the return path fromsecond control grid 112 to ground;

tron stream projected through the accelerating electrode is varied inaccordance withan input signal, the charge density of 'the virtualcathode is varied in a correspond ing manner, and if a suitableinductive load is connected to the low-potential control grid, anamplified replica of the input signal is'induced at the control grid byspace charge coupling from the input grid. This space charge I couplingeffect has been formally likened to a unilateral negative capacityhaving a magnitude of the order of a few mrcro-microfarads Because it isunilateral in nature, it may be considered as providing aneffectivetrans- .conductance from the input grid to the low-potential controlgrid having a magnitude'of ZarfC, where f is the input-signal frequencyand C is the equivalent space charge coupling capacity. a

In order to provide intermediate-frequency amplification between firstcontrol 110 and second control grid 112, therefore, the impedance oftwo-terminal load circuit, comprising inductor 122 and shunt capacity123, at

the intermediate-frequency ismade greater than the recrprocal of theeffective transconductance, at the intermedrate-frequency, of firstcontrol grid 110 with respect to second control grid 112. Sinceamplification may be computed as the product of the etfectivetransconductance and the load impedance, as is well known in the art,amplification or gain greater than unity is 'thus achieved. In practice,ratios of'load impedance to reciprocal effective transconductance muchgreater than unity are preferred; for example, ratios of 10 or more havebeen employed with eminent success.

Inductor 122 and cfiective shunt capacity 123 are tuned to theintermediate frequency to provide therequisite impedance at thefrequencies of the carrier components J V I I Consequently, thevideo-carrier and sound-carrier components appear in however, it maybepossible by judicious design of the tube to operate second control grid112 atzero bias, in which event the biasing means may consist of adirect connection between terminal 128 and cathode 109. I Consequently,the video-carrier and audio-modulated sound-. carrier components of theamplified signal appearingat second control grid 112 are subjected toanode-bend detection and are intermodulated by device 108 to provide anaudio-modulated signal having a carrienfrequency corresponding to thefrequency separation between the video-carrier and sound-carriercomponents. 1 Load .cir-

cuit 130, 131 is tuned to, the intercarrier frequency, and

amplified intercarrier sound signals are developed at" anode 113 byvirtue of the transconductance characteristic of second control grid 112with respect to anode 113.

These intercarrier signals, bearing the audio modulation,

are applied to limiter-discriminator 105 where they are detected toprovide audio-frequency signals which are applied, after suitableamplification, to loudspeaker 107.

Resistor 125 and condenser 126, having a time constant 7 which is shortwith respect to the highest-audio-frequency.

components, are preferably included'in the circuit from second controlgrid 112 to cathode 109. Resistor-condenser network 125, 126 provides anautomatic variation in the bias of second control grid 112 in accordancewith the audio-frequency modulation components, thus tending to preventthe amplified intermediate-frequency sig-.

nals from driving the second control grid beyond its linear operatingrange 'and thus avoiding undesirable modulation of the intercarn'ersoundsignals by changes in picture carrier level in accordance'with thevideo and synchronizing components.

in the illustrated embodiment of the invention, amplification of themodulated-carrier input signals is accomplished by virtue of spacecharge coupling between two control grids separated by an acceleratingelectrode Means associated with the. second control grid are providedfor efiec'ting demodulation of the amplified replica of the input signaland for modulating the electron flow to the output electrode of the tubein accordance with modulation components of the amplified replica. Thesemodulation components. are then amplified by virtue of thetransconductance of the second control grid with respect to the finalanode'or output electrode. detection gain is proportional to thetransconductance of the second control grid with respect to the anode.If desired, a separate rectifier may be employed for detection,

' in the manner described in application Serial No.

305,875, in which event the overall conversionjgain is proportional tothe transconductance or first derivative of anode current with respectto second-control-grid voltage at the operating point; in embodimentsemploying anodebend detection at the second control grid, the overallconversion gain is proportional to the first derivative of: thattransconductance or second derivative of anode current with respect tosecond-control-grid voltage, which is a measure of the degree'ofnon-linearity of the dynamic transfer characteristic at the operatingpoint.

Thus, the invention provides new and improved wave signal translatingapparatus for effectively accomplish: ing in a single stage the severalfunctions of input-signal The postamplification, demodulation, andsubsequent amplification of the modulation components. While theinvention has been shown and described in the environment of atelevision receiver, it may also be used to advantage in other types ofmodulated wave-signal translating apparatus such as ultra-high frequencyamplitude-modulation receivers. However, since the invention isdependent on the advantageous use of the space charge coupling effect,which is of useful magnitude only at relatively high frequencies, itsutility is limited to applications at frequencies of the order of 1megacycle or higher.

While a particular embodiment of the present invention has been shownand described, it is apparent that numerous variations and modificationsmay be made, and it is therefore contemplated in the appended claims tocover all such variations and modifications as fall with in the truespirit and scope of the invention.

I claim:

1. Wave-signal translating apparatus comprising: an electron-dischargedevice including, in the order named, a cathode, a first control grid,an accelerating electrode, a second control grid and an outputelectrode; a source of composite television signals, includingvideo-modulated image-carrier and audio-modulated sound-carriercomponents separated by a predetermined frequency difference, coupled toone of said control grids and to said cathode; a two-terminal loadcircuit having one terminal coupled externally of said device to theother of said control grids only and having an impedance at thefrequencies of said image-carrier and said audio-modulated sound-carriercomponents greater than the reciprocal of the effectivetransconductance, at said frequencies, of said one control grid withrespect to said other control grid for developing an amplified signalincluding said carrier components; means coupled to said other controlgrid and to said cathode for elfecting demodulation of said amplifiedsignal, whereby said image-carrier and said audio-modulatedsound-carried components of said amplified signal are intermodulated;means, including an output circuit tuned to an intercarrier frequencycorresponding to said predetermined frequency difference, coupled tosaid output electrode and to said cathode and utilizing thetransconductance of said other control grid with respect to said outputelectrode for developing an amplified audio-modulatedintercarrier-frequency output signal and means coupled to said outputcircuit for demodulating said audio-modulated output signal.

2. Wave-signal translating apparatus comprising: an electron-dischargedevice including, in the order named, a cathode, a first control grid,an accelerating electrode, a second control grid, and an outputelectrode; a source of composite television signals, includingvideo-modulated image-carrier and audio-modulated sound-carriercomponents separated by a predetermined frequency difference, coupled tosaid first control grid and to said cathode; a two-terminal load circuithaving one terminal coupled externally of said device to said secondcontrol grid only and having an impedance at the frequencies of saidimage-carrier and said audio-modulated soundcarrier components greaterthan the reciprocal of the effective transconductance, at saidfrequencies, of said first control grid with respect to said secondcontrol grid for developing an amplified signal including said carriercomponents; means coupled to said second control grid and to saidcathode for eiiecting demodulation of said amplified signal, wherebysaid image-carrier and said audiomodulated sound-carrier components ofsaid amplified signal are intermodulated; means, including an outputcircuit tuned to an intercarrier frequency corresponding to saidpredetermined frequency difierence, coupled to said output electrode andto said cathode and utilizing the transconductance of said secondcontrol grid with respect to said output electrode for developing anamplified audio-modulated intercarrier-frequency output signal and meanscoupled to said output circuit for demodulating said audio-modulatedoutput signal.

3-. Wave-signal translating apparatus comprising: an electron-dischargedevice including, in the order named, a cathode, a first control grid,an accelerating electrode, a second control grid, and an outputelectrode; a source of composite television signals, includingvideo-modulated image-carrier and audio-modulated sound-carriercomponents separated by a predetermined frequency difference, coupled tosaid first control grid and to said cathode; a two-terminal load circuithaving one terminal coupled externally of said device to said secondcontrol grid only and having an impedance at the frequencies of saidimage-carrier and said audio-modulatedv soundc'arrier components greaterthan the reciprocal of the effective transconductance, at suchfrequencies, of said first control grid with respect to said secondcontrol grid for developing an amplified signal including said carriercomponents; means coupled to said second control grid and to saidcathode for biasing said second control grid to a non-linear portion ofits dynamic transfer characteristic, whereby said imagecarrier and saidaudio-modulated sound-carrier components of said amplified signal areintermodulated by said device; means, including an output circuit tunedto an intercarrier frequency corresponding to said predeterminedfrequency difference, coupled to said output electrode and to saidcathode and utilizing the transconductance of said second control gridwith respect to said output electrode for developing an amplifiedaudiomodulated intercarrier-frequency output signal and means coupled tosaid output circuit for demodulating said audio-modulated output signal.

4. Wave-signal translating apparatus comprising: an electron-dischargedevice including, in the order named, a cathode, a first control grid,an accelerating electrode, a second control grid and an outputelectrode; a source of composite television signals, includingvideo-modulated image-carrier and audio-modulated sound-carriercomponents separated by a predetermined frequency difference, coupled toone of said control grids and to said cathode; a double-tunedtwo-terminal load circuit exhibiting a double-peaked impedancecharacteristic hav ing one terminal coupled externally of said device tothe other of said control grids only and having an impedance at thefrequencies of said image-carrier and said audiomodulated sound-carriercomponents greater than the reciprocal of the effectivetransconductance, at said frequencies, of said one control grid withrespect to said other control grid for developing an amplified signalincluding said carrier components; means coupled to said other controlgrid and to said cathode for effecting demodulation of said amplifiedsignal, whereby said imagecarrier and said audio-modulated sound-carriercomponents of said amplified signal are intermodulated; means, includingan output circuit tuned to an intercarrier frequency corresponding tosaid predetermined frequency difference, coupled to said outputelectrode and to said cathode and utilizing the transccnduct'ance ofsaid other control grid with respect to said output electrode fordeveloping an amplified audio-modulated intercarrier-frequency outputsignal and means coupled to said output circuit for demodulating saidaudio-modulated output signal.

References Cited in the file of this patent UNITED STATES PATENTS2,616,036 Adler Oct. 28, 1952

